First off, I'm running Rasbian with NOOBS.
I was following a tutorial on creating a new partition here: How do I create and mount a partition using the remainder of my SD card? And I started wondering why there's un-partitioned space on the sd card to begin with? Can I count on this always to be the case if I install Raspbian using NOOBS? Or should it be expected that the root partition takes up the entire remaining space? Thanks in advance.
Info for accepted answer
The reason I asked this question is because I'm updating a fleet of raspberry pi's remotely. Part of my update requires making a new partition on the disk. I am worried that the method I cited won't work for every SD card on my devices even though they are cloned from the same image. It worked for the SD card I'm testing on but how do I know there will be unpartitioned space on EVERY card?
The answer below tells me basically... it's not guaranteed and also resizing the root file system is impossible without unmounting it I believe. So basically I can either first see if there is unpartitioned space and apply the update, or get notified that a certain device can't be updated... shoot
@crasic pointed out that it is possible to resize the root partition via the boot parameters in /boot/config.txt. See his link in his answer